A thermoplastic resinous composite material is molded into panel boards and parts by a molding technique such as an extrusion molding and an injection molding. Talc or calcium carbonate may be used as an additive material to be contained in the composite material in order to improve the physical property of a product molded using the composite material. Mica is also widely used as such an additive material.
In general, the shape of mica is flat, and it is known that mica is well dispersed in a meltage of the composite material during a molding process and is orientated along a surface of a product molded using the composite material (see FIG. 2) and is also known that the product made from the composite material containing mica is excellent in the tensile strength, the flexural strength, the flexural elasticity and the H.D.T. Thus, less than 800 .mu.m in weight average flake size and 30-50 in weight average aspect ratio of mica is contained in the thermoplastic resinous composite material.
Also, it is well known that a composite material made from a mixture of polypropylene and a wood cellulose filler, such as a wood powder and a paper, is used for an extrusion molding.
The wood cellulose filler mixed is obtained by grinding a wood material in about 40-200 mesh. This wood cellulose filler contains large a large quantity of cylindrical fragments and a small quantity of granulous fragments, as shown in FIG. 1 (FIG. 1 is a rough sketch of a wood powder magnified by a microscope).
In a molding process which uses a composite material made from a mixture of such a wood cellulose filler and an olefin series plastic, the wood cellulose filler is strongly orientated in a flow direction (i.e. a meltage of the composite material is flowing in the flow direction and is simultaneously molded) so as to cause differences in magnitude of the tensile strength, the flexural strength, the flexural elasticity and the impact resistance between the flow direction and a direction perpendicular to the flow direction, so that a product molded using such a composite material is warped and distorted.
In addition, the tensile strength and the flexural elasticity of the product are excellent in the flow direction, because the wood cellulose filler is strongly orientated in the flow direction. However, if the amount of the wood cellulose filler added is increased, the fragility of the product is increased i.e. the impact resistance thereof is considerably reduced.
In addition, the shape of each fragment of the ground wood cellulose filler is uneven and the surface thereof has irregularities so as to easily hitch. However, if the wood cellulose filler is mixed together with the olefin series plastic having a smooth surface, fragments of the wood cellulose filler and particles of the olefin series plastic are separated from each other by vibrations caused when the mixture is falling down from a hopper (located at a section for supplying the composite material to a molding machine) to a screw section, so that the mix proportion is changed.
In addition, while the wood cellulose filler is melted and mixed together with the olefin series plastic in the screw section, the wood cellulose filler is not well dispersed in a meltage of the composite material in comparison with inorganic fillers. Thus, if a composite material containing such a wood cellulose filler is used, the physical property to be exhibited in each product molded may be different and is often largely differed.
As discussed above, the additive material and the filler are very effective materials for improving the physical property of the product such as the tensile strength, the flexural strength, the flexural elasticity and the H.D.T. However, the good impact resistance of the product can not be achieved in simultaneous with those physical properties.
Several methods have been provided for achieving the good impact resistance in simultaneous with achieving the good tensile strength, the good flexural elasticity and the good H.D.T.
For example, there is a method which improves the impact resistance by undergoing a rubber-modification process to modify the olefin series plastic into ethylene-modified-polypropylene in a composite material made from a mixture consisting of the olefin series plastic and an inorganic material such as talc, calcium carbonate and the like. However, in this method, the flowability of a meltage of the composite material during a molding process is reduced and the cost is essentially high so that this method is not practical.
In European Patent No. 0319589 (corresponding to Japanese Patent Publication No. Showa 60(1985)-40965 entitled "Method and Apparatus for producing Panel"), in a composite material made from a mixture mainly consisting of a wood cellulose filler such as a wood powder and an olefin series plastic, fiber flax is used in combination therewith. In this method, the impact resistance to be achieved in a product molded using the composite material is excellent. However, the flexural elasticity of the product and the flowability of a meltage of the composite material during a molding process are considerably reduced.
In addition, in Japanese Patent Publication No. Showa 57(1982)-43575entitled "Composite Material using Paper and Method for producing same", in a composite material made from a mixture mainly consisting of a wood cellulose filler such as a paper and an olefin series plastic, a natural or synthetic rubber is used in combination therewith. In this method, the impact resistance is improved by elastomer. However, the cost is high, the flowability of a meltage of the composite material during a molding process is considerably low, and the productivity is low.
As discussed above, in a composite material made from a mixture of an olefin series plastic and an inorganic filler such as talc or an organic filler such as a wood cellulose, the physical property exhibited in a product molded using the composite material is excellent in the tensile strength, the flexural strength, the flexural elasticity and the H.D.T, and such excellent properties can be easily provided for the product by controlling the amount and the size of the filler to be added. However, the impact resistance of the product is reduced. In other words, as improving the impact resistance, not only the physical property such as flexural elasticity and the like but also the flowability of a meltage of the composite material during a molding process are considerably reduced.
This is because the physical property such as the tensile strength, the flexural elasticity and the H.D.T is, in general, contrary to the impact resistance of the product and the flowability of the composite material during a molding process.
Thus, it has been believed that it is difficult to provide a thermoplastic resinous composite material which has the good flowability of a meltage of the composite material during the molding process and which can provide the good flexural strength, the good flexural elasticity, and the good H.D.T for a product molded using the composite material and can also achieve the good impact resistance.
The present invention is made in view of those matters discussed above. An object of the present invention is to provide a thermoplastic resinous composite material which has the good flowability of a meltage of the composite material during the molding process and which can provide the good flexural strength, the good flexural elasticity, and the good H.D.T for a product molded using the composite material and can also achieve the good impact resistance which can not be achieved by a composite material of the art.
Another object of the present invention is to provide the above composite material suitable for use in an extrusion molding, a compression molding, a transfer molding and a blow molding.
Still another object of the present invention is to provide the above composite material usable for an injection molding.